It’s a program called musikCube (link) – like WMP, it has media library functionalities, but unlike WMP, it uses very little system resource (about 1 – 2% of a 3GHz P4 HT CPU) and about 10 MB of RAM on normal usage (5 MB on startup).

Here’re some of the other features I really like / find useful:

• Supports FLAC, OGG Vorbis, WMA, MP3 (just to name a few).

• It uses SQLite as the backend database engine – so you can go nuts in modifying the database outside of the program’s UI!